WO2020091426A1 - Lithium electrode and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a lithium electrode and a lithium secondary battery comprising same. More specifically, the lithium electrode comprises a protective layer, in which an ion conductive electrolyte is contained in the inside and surface of an electrically conductive matrix, wherein the protective layer can equalize the electrical conductivity in the surface of the lithium electrode, physically prevent the growth of lithium dendrites by exerting strength during the growth of lithium dendrites, and suppress the generation of dead lithium.

Description

Lithium electrode and lithium secondary battery comprising the same

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0130444 filed on October 30, 2018 and Korean Patent Application No. 10-2019-0136807 filed on October 30, 2019. All content disclosed in the literature is included as part of this specification.

The present invention relates to a lithium electrode having a uniform electrical conductivity on a lithium metal surface and a lithium secondary battery comprising the same.

Until recently, there has been considerable interest in developing high energy density cells using lithium as the negative electrode. Lithium metal compared to other electrochemical systems with lithium intercalated carbon anodes, and nickel or cadmium electrodes, for example, reducing the energy density of the cell by increasing the weight and volume of the anode in the presence of a non-electroactive material Since it has low weight and high capacity characteristics, it is very interesting as a negative electrode active material for electrochemical cells. A lithium metal negative electrode, or a negative electrode mainly containing lithium metal, provides an opportunity to construct a lighter and higher energy density battery than a battery such as a lithium-ion, nickel metal hydride, or nickel-cadmium battery. These features are highly desirable for batteries for portable electronic devices such as cell phones and laptop computers, where the premium is paid at low weight.

Conventional lithium ion batteries have an energy density of 700 wh / l using graphite as a cathode and lithium cobalt oxide (LCO) as a cathode. However, in recent years, fields requiring high energy density have been expanded, and the need to increase the energy density of lithium ion batteries has been continuously raised. For example, it is necessary to increase the energy density to increase the mileage to 500 km or more per charge of an electric vehicle.

The use of lithium electrodes is increasing to increase the energy density of lithium ion batteries. However, lithium metal is a metal that is highly reactive and difficult to handle, which is difficult to handle in a process.

When a lithium metal is used as the negative electrode of a lithium secondary battery, the lithium metal reacts with impurities such as an electrolyte, water or an organic solvent, and a lithium salt to form a solid electrolyte interphase (SEI). Such a passivation layer causes a difference in the current density on the local area, promotes the formation of dendritic dendrites by lithium metal during charging, and gradually grows during charging and discharging to cause an internal short circuit between the anode and the cathode. In addition, dendrites have a mechanically weak neck (bottle neck), thereby forming dead lithium that loses electrical contact with the current collector during discharge, thereby reducing the capacity of the battery, shortening the cycle life, and stability of the battery. Has a bad effect on

In order to improve the problems of the lithium metal negative electrode, a lithium metal negative electrode having a protective layer having various compositions or forms has been developed.

Korean Patent Publication No. 2012-0000708 relates to a negative electrode for an electrochemical device, and discloses a porous conductive coating layer formed on a negative electrode active material layer, wherein the porous conductive coating layer is conductive particles (ex, carbon black, acetylene black, carbon fiber, etc.) It suggests a form bound to each other by a binder.

Korean Patent Publication No. 2018-0036564 relates to a negative electrode for a lithium secondary battery comprising a lithium metal layer and a protective layer, wherein the protective layer is a conductive fabric with pores formed thereon, wherein the conductive fabric has a metal material on a base fabric woven with yarn. It presents a composition that is a coated conductive fabric.

As described above, until now, in a battery using a lithium metal anode, research has been conducted on the development of a protective layer to prevent dendrite growth of lithium metal, but research results on the protective layer enabling improvement of overall battery performance are insufficient. to be.

Therefore, in a battery using lithium metal as a negative electrode, in order to improve battery performance, it is urgent to develop a lithium metal negative electrode that exhibits uniform electrical conductivity at the electrode surface to suppress the growth of lithium dendrites and prevent the occurrence of dead Li. to be.

[Advanced technical literature]

[Patent Document]

(Patent Document 1) Korean Patent Publication No. 2012-0000708

(Patent Document 2) Korean Patent Publication No. 2018-0036564

As a result of various studies to solve the above problems, the present inventors formed a protective layer on a lithium electrode, but formed a protective layer in the form of containing an ion conductive electrolyte on the inside and the surface of the electrically conductive matrix. , It was confirmed that the electrical conductivity of the surface of the lithium electrode was uniform, and the growth of lithium dendrites could be suppressed and the generation of dead Li could be suppressed due to the strength of the protective layer.

Accordingly, an object of the present invention is to provide a lithium electrode having uniform electrical conductivity.

In addition, another object of the present invention is to provide a lithium secondary battery comprising a lithium electrode having a uniform electrical conductivity as described above.

In order to achieve the above object, the present invention, lithium metal: and a lithium layer comprising a protective layer formed on at least one side of the lithium metal, wherein the protective layer comprises an electrically conductive matrix and an ion conductive electrolyte, lithium Provide an electrode.

The present invention also provides a lithium secondary battery containing the lithium electrode.

According to the present invention, the lithium electrode includes a protective layer, and the protective layer has an effect in which the electrical conductivity of the lithium electrode surface is uniform due to the structure in which the ion conductive electrolyte is formed on the inside and the surface of the electrically conductive matrix. have.

In addition, the growth of lithium dendrites can be suppressed as the electrical conductivity of the surface of the lithium electrode is uniform.

In addition, since the protective layer is formed while maintaining an appropriate strength on the surface of the lithium electrode, it is possible to further enhance the lithium dendrite growth suppression effect, thereby preventing the occurrence of dead lithium.

1 is a schematic view comparing the form of lithium dendrites according to the presence or absence of a protective layer of a lithium electrode.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

Lithium electrode

The present invention relates to a lithium electrode comprising: a lithium metal: and a protective layer formed on at least one surface of the lithium metal, wherein the protective layer may include an electrically conductive matrix and an ion conductive electrolyte.

In the present invention, the electrically conductive matrix may be in the form of a three-dimensional structure in which an internal space is formed. The interior space may be referred to as pore.

An ion conductive electrolyte may be filled in the inner space of the electrically conductive matrix, and the electrically conductive matrix may be surrounded by the ion conductive electrolyte, that is, the ion conductive electrolyte may be formed on the surface of the electrically conductive matrix. It might be.

Due to this form of the protective layer, the electrical conductivity can be made uniform on the surface of the lithium electrode, so that the growth of lithium dendrites can be suppressed.

In addition, due to the strength of the protective layer itself, the growth of lithium dendrites can be suppressed, thereby preventing the occurrence of dead lithium in electrical contact.

In addition, in the protective layer, the weight ratio of the ion conductive polymer contained in the electrically conductive matrix and the ion conductive electrolyte may be 3: 7 to 7: 3. When the electrically conductive matrix exceeds the prescribed weight range as described above, the content of the ion-conducting polymer is relatively reduced, so the Li ion conductivity of the protective layer is very low, and more Li grows on the protective layer, resulting in the growth of Li dendrites. It is difficult to suppress. Conversely, if the electrically conductive matrix is outside the prescribed weight range as described above and is smaller than the appropriate weight, vertical / horizontal electrical conductivity may be lowered and uniform electron transfer to the electrode surface may be difficult.

When the ion conductive electrolyte is liquid or gel, the ion conductive polymer may contain about 25 to 50% by weight of the electrolyte. In other words, the electrolyte uptake amount may be 25 to 50% by weight relative to 100% by weight of the ion conductive polymer, and lithium ion conductivity may be best within this range.

In addition, when the ion-conducting electrolyte is in a solid phase, the ion-conducting electrolyte may include 25 to 50% by weight of the remaining components excluding the solvent in the electrolyte together with the ion-conducting polymer. In other words, compared to 100% by weight of the ion conductive polymer, the content of the remaining components excluding the solvent in the electrolyte may be 25 to 50% by weight. At this time, the remaining components other than the solvent in the electrolyte may be a lithium salt and an additive.

In the present invention, the sheet resistance of the protective layer is 5 x 10 ^-2 Ω / sq. To 1000 Ω / sq., Preferably ¹ × 10 ^-2 Ω / sq. To about 500 Ω / sq, more preferably from ^{1 x 10 -. 2 Ω /} sq. To 300 Ω / sq. If it is less than the above range, it is difficult to suppress the growth of Li dendrites because there is more Li growing on the protective layer, and if it is above the range, the life characteristics of the battery may be deteriorated by acting as a large resistance layer.

In the present invention, the vertical lithium ion conductivity of the protective layer is 1x10 ^-6 S / cm to 1x10 ^-2 S / cm at room temperature, preferably 1x10 ^-5 S / cm to 1x10 ^-2 S / cm, more preferably May be 1x10 ^-4 S / cm to 1x10 ^-2 S / cm. If it is less than the above range, the vertical ion conductivity is not good, so there is more Li growing on the protective layer, so it is difficult to suppress the growth of Li dendrites, and a protective layer exceeding the above range cannot be formed.

In the present invention, the electrically conductive material included in the electrically conductive matrix is uniformly distributed while forming a three-dimensional structure throughout the electrically conductive matrix, so that the protective layer can exhibit uniform electrical conductivity.

The electrically conductive material may be at least one selected from the group consisting of electrically conductive metals, semiconductors, and electrically conductive polymers. The electrically conductive metal may be at least one selected from the group consisting of copper, gold, silver, aluminum, nickel, zinc, carbon, tin and indium. The semiconductor may be one or more selected from the group consisting of silicon and germanium. The electrically conductive polymer is PEDOT (poly (3,4-ethylenedioxythiophene)), polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene and polyphenylene It may be at least one selected from the group consisting of poly (thienylene vinylene).

In the present invention, the ion conductive electrolyte contained in the electrically conductive matrix may include an ion conductive polymer.

The ion-conducting polymer includes polyethylene oxide (Poly (ethylene oxide): PEO), polypropylene oxide (Poly (polypropylene oxide: PPO), polyacrylonitrile (PAN)) and polyvinylidene fluoride (Poly ( vinylidene fluoride): PVDF).

In addition, the ion-conducting electrolyte may be in a liquid, gel or solid phase. The form of such an ion-conducting electrolyte may be determined according to the properties of the ion-conducting polymer.

For example, the ion-conducting polymer is (i) an ion-conducting polymer that exhibits a swelling characteristic by an electrolyte, or (ii) has an ethylene oxide group (EO group), thereby providing ion-conducting properties by itself. It may be a polymer.

The polymer having the characteristic that the ion-conducting polymer is swelled by the electrolyte (i) can be impregnated with a liquid or gel-like electrolyte to form a liquid or gel-like ion-conducting electrolyte. PVDF is an example of such a polymer.

The ion-conducting polymer (ii) a polymer having an ethylene oxide group (EO group) can form a solid ion-conducting electrolyte with a lithium salt and additional additives without a separate solvent. PEO is an example of such a polymer.

The liquid or gel electrolyte contained in the liquid or gel ion conductive electrolyte may further include a lithium salt, a non-aqueous solvent, and additional additives. The solid phase ion conductive electrolyte may further include a lithium salt and additional additives.

The lithium salt is LiCl, LiBr, LiI, LiNO ₃ , LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, 4-phenyl lithium borate And it may be one or more selected from the group consisting of lithium imide.

In addition, as the non-aqueous solvent included in the ion conductive electrolyte, those commonly used in electrolytes for lithium secondary batteries can be used without limitation, for example, ether, ester, amide, linear carbonate, cyclic carbonate, etc., respectively, alone or It can be used by mixing two or more kinds. Among them, a cyclic carbonate, a linear carbonate, or a carbonate compound that is a slurry thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and any one selected from the group consisting of halides, or a slurry of two or more of them. Examples of these halides include, but are not limited to, fluoroethylene carbonate (FEC).

In addition, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate or these Among them, two or more kinds of slurries may be used, but are not limited thereto. Particularly, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so that lithium salts in the electrolyte can be better dissociated, such as dimethyl carbonate and diethyl carbonate. When a low-viscosity, low-permittivity linear carbonate is mixed and used in an appropriate ratio, an electrolyte having a higher electrical conductivity can be prepared.

In addition, as the ether in the non-aqueous solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether, or two or more of them may be used. , But is not limited thereto.

Further, among the non-aqueous solvents, esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, and γ-caprolactone. , σ-valerolactone and ε-caprolactone, any one selected from the group or two or more of them may be used, but is not limited thereto.

In addition, the additive included in the ion conductive electrolyte may be at least one selected from the group consisting of fluoroethylene carbonate (FEC), 1,3-propanesultone (1,3-PS) and vinyl ethylene carbonate (VEC), , Preferably fluoroethylene carbonate (FEC).

The content of the additive may be 2 to 13% by weight, preferably 3 to 10% by weight, more preferably 4 to 8% by weight based on the total weight of the electrolyte. If it is within the above range, the life characteristics of the lithium secondary battery can be improved, and the thickness expansion rate of the lithium secondary battery can be reduced.

As described above, the lithium electrode including the protective layer including the electrically conductive matrix and the ion conductive electrolyte is a lithium dendrite. Growth can be prevented.

1 is a schematic view comparing the form of lithium dendrites according to the presence or absence of a protective layer of a lithium electrode.

Referring to FIG. 1, in the case of a lithium electrode without a protective layer, a solid electrolyte interphase (SEI) layer formed at an interface between a native oxide layer on the surface of the lithium metal 10 and an electrolyte 30 is formed, and the It can be seen that the oxide layer and the electrical conductivity of the surface of the lithium metal 10 are locally non-uniform in the case of the SEI, which is electrically nonconductive, which causes lithium dendrite growth.

On the other hand, in the case of the lithium electrode having the protective layer including the electrically conductive matrix and the ion conductive electrolyte as described above, lithium dendrite growth is suppressed due to the protective layer 20 formed on the surface of the lithium metal 10.

Manufacturing method of lithium electrode

The present invention also relates to a method for manufacturing a lithium electrode.

The method for manufacturing a lithium electrode according to the present invention may vary depending on the form of the ion conductive electrolyte contained in the protective layer formed on the lithium electrode. Depending on the properties of the ion-conducting polymer contained in the ion-conducting electrolyte, the ion-conducting electrolyte may be divided into a liquid phase or a gel phase and a solid phase, and a method of manufacturing a lithium electrode is different depending on the type of the ion-conducting electrolyte. can do.

Liquid or Gel  Method for manufacturing a lithium electrode having a protective layer containing an ion conductive electrolyte

In the present invention, a method of manufacturing a lithium electrode having a protective layer including a liquid or gel-like ion conductive electrolyte includes: (S1) forming an ion conductive polymer layer by applying an ion conductive polymer to a release film; (S2) depositing an electrically conductive material on the ion conductive polymer layer to form an electrically conductive matrix inside the ion conductive polymer layer; (S3) transferring the ion conductive polymer layer on which the electrically conductive matrix is formed on a lithium metal to form a lithium electrode; And (S4) impregnating the lithium electrode with an electrolyte to form a protective layer including an electrically conductive matrix and an ion conductive electrolyte.

In the step (S1), an ion-conducting polymer layer may be formed by applying an ion-conducting polymer to the release film.

The material and thickness of the release film are not particularly limited, and various films may be used. As the release film, for example, a polyethylene terephthalate (PET) film, a polyethylene (PE) film, a polypropylene (PP) film, a silicone-based release film, etc. can be used, and the release film thickness is, for example, 12 μm to 80 μm.

In addition, the ion-conducting polymer is not particularly limited as long as it is a polymer that exhibits a swelling characteristic by an electrolytic solution, and may be, for example, polyvinylidene fluoride (PVDF).

The thickness of the ion conductive polymer layer is not particularly limited, for example, 100 nm to 1 μm, preferably 150 nm to 300 nm can be formed to a suitable thickness in the range.

The method for forming the ion conductive polymer layer may use various coating methods that can be used to form a coating layer in the art. For example, the coating method includes dip coating, spray coating, spin coating, die coating, roll coating, and slot-die coating. ), Bar coating (Bar coating), gravure coating (Gravure coating), comma coating (Comma coating), curtain coating (Curtain coating) and micro-gravure coating (Micro-Gravure coating).

In addition, after coating, the ion conductive polymer may be prepared as a coating solution, and then coated.

In addition, the solvent used in preparing the coating solution is tetrahydrofuran (THF), toluene, cyclohexane, N-methyl-2-pyrrolidone (N-methyl-2-pyrolidone, NMP) , Dimethyl Formamide (DMF), Dimethyl Acetamide (DMAc), Tetramethyl Urea, Dimethyl Sulfoxide (DMSO) and Triethyl Phosphate It may be one or more selected.

In addition, the concentration of the ion-conducting polymer in the coating solution may be 1 to 15% by weight, preferably 2 to 10% by weight, more preferably 3 to 8% by weight. If it is less than the above range, the protective function of lithium metal may be deteriorated, and if it is above the above range, the concentration of the coating solution may be excessively high, making it difficult to proceed with the coating process, and even if a protective layer is formed, cracks may occur.

In addition, the solvent used in preparing the coating solution is tetrahydrofuran (THF), toluene, cyclohexane, N-methyl-2-pyrrolidone (N-methyl-2-pyrolidone, NMP) , Dimethyl Formamide (DMF), Dimethyl Acetamide (DMAc), Tetramethyl Urea, Dimethyl Sulfoxide (DMSO) and Triethyl Phosphate It may be one or more selected. Preferably, when THF is used in preparing the coating solution, the solubility of the electrically conductive matrix is high and it may be advantageous to form a protective layer by a coating process.

The ion conductive polymer layer may exhibit a porous form.

In the step (S2), an electrically conductive material may be deposited on the ion conductive polymer layer to form an electrically conductive matrix inside the ion conductive polymer layer.

At this time, in the electrically conductive material, particles of the electrically conductive material penetrate the ion conductive polymer layer during deposition, and particles of the electrically conductive material are inserted into the ion conductive polymer layer. The particles of the electrically conductive material inserted into the ion-conducting polymer layer may be in the form of an island or may be connected to each other to form a skeleton of a three-dimensional structure to form an electrically conductive matrix, The island shape and the 3D structure may be formed together.

In other words, it may be a form in which an ion conductive polymer is included in the inner space of the electrically conductive matrix, or an ion conductive polymer may be formed on the surface of the electrically conductive matrix to surround the electrically conductive matrix.

In the step (S3), the ion conductive polymer layer on which the electrically conductive matrix is formed may be transferred onto a lithium metal to form a lithium electrode.

The lithium metal may be formed on a current collector. The current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the current collector may be one or more selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, and calcined carbon.

In the step (S4), the lithium electrode may be impregnated with an electrolyte solution to form a protective layer including an electrically conductive matrix and an ion conductive electrolyte.

The electrolyte solution includes a lithium salt and a non-aqueous solvent, and may further include an additive, and the specific composition of the electrolyte solution is as described above.

When the lithium electrode is impregnated with an electrolyte, the electrolyte may permeate the ion conductive polymer to form an ion conductive electrolyte. At this time, the ion-conducting electrolyte may be liquid or gel.

Accordingly, the lithium electrode may be manufactured to include a protective layer including an electrically conductive matrix and an ion conductive electrolyte on lithium metal.

Solid phase ion conductivity  Method for manufacturing a lithium electrode having a protective layer containing an electrolyte

In the present invention, a method of manufacturing a lithium electrode having a protective layer including a solid ion conductive electrolyte includes: (P1) forming an ion conductive electrolyte layer by coating a release film with a mixture of an ion conductive polymer and a lithium salt; (P2) depositing an electrically conductive material on the ion conductive electrolyte layer to form a protective layer including an electrically conductive matrix and an ion conductive electrolyte; And (P3) transferring the protective layer onto the lithium electrode.

In the step (P1), an ion conductive electrolyte layer may be formed by coating a release film with a mixture of an ion conductive polymer and a lithium salt. At this time, an additive may be additionally mixed with the mixture, and the lithium salt and the additive may be the same as the lithium salt and the additive included in the electrolyte solution as described above.

The method and thickness of forming the ion conductive electrolyte layer may be the same as the method and thickness of forming the ion conductive polymer layer described above.

Further, the ion conductive electrolyte layer may be in a solid phase.

In the step (P2), an electrically conductive material may be deposited on the ion conductive electrolyte layer to form a protective layer including an electrically conductive matrix and an ion conductive electrolyte.

At this time, in the electrically conductive material, particles of the electrically conductive material penetrate the ion conductive electrolyte layer during deposition, and particles of the electrically conductive material are inserted into the ion conductive electrolyte layer. The particles of the electrically conductive material inserted into the ion conductive electrolyte layer may be in the form of an island, or particles may be connected to each other to form a skeleton of a 3D structure to form an electrically conductive matrix, The island shape and the 3D structure may be formed together.

In other words, an ion conductive electrolyte may be included in the inner space of the electrically conductive matrix, or an ion conductive electrolyte may be formed on the surface of the electrically conductive matrix to surround the electrically conductive matrix.

In the step (P3), the protective layer may be transferred onto a lithium metal to form a lithium electrode.

The lithium electrode may be a structure including a protective layer including an electrically conductive matrix and an ion conductive electrolyte on lithium metal.

Lithium secondary battery

The present invention also relates to a lithium secondary battery comprising a lithium electrode as described above.

In the lithium secondary battery, the lithium electrode may be included as a negative electrode, and the lithium secondary battery may include an electrolyte solution provided between the negative electrode and the positive electrode.

The shape of the lithium secondary battery is not limited, and may be, for example, coin, flat, cylindrical, horn, button, sheet or stacked. In addition, the lithium secondary battery may further include a tank for storing the positive electrode electrolyte and the negative electrode electrolyte, and a pump that moves each electrolyte solution to the electrode cell, and may be manufactured as a flow battery.

The electrolyte solution may be an electrolyte solution impregnated with the negative electrode and the positive electrode.

The lithium secondary battery may further include a separator provided between the negative electrode and the positive electrode. The separator positioned between the negative electrode and the positive electrode may be used as long as it separates or insulates the negative electrode and the positive electrode from each other and enables ion transport between the negative electrode and the positive electrode. For example, it may be a non-conductive porous film or an insulating porous film. More specifically, a polymer nonwoven fabric such as a nonwoven fabric of polypropylene material or a nonwoven fabric of polyphenylene sulfide material; Alternatively, a porous film of an olefin-based resin such as polyethylene or polypropylene can be exemplified, and it is also possible to use two or more of these together.

The lithium secondary battery may further include a positive electrode electrolyte on the positive electrode side and a negative electrode electrolyte on the negative electrode side separated by a separator. The positive electrode electrolyte and the negative electrode electrolyte may each include a solvent and an electrolytic salt. The positive electrode electrolyte and the negative electrode electrolyte may be the same as or different from each other.

The electrolyte solution may be an aqueous electrolyte solution or a non-aqueous electrolyte solution. The aqueous electrolyte solution may include water as a solvent, and the non-aqueous electrolyte solution may include a non-aqueous solvent as a solvent.

The non-aqueous solvent may be selected to be generally used in the art, and is not particularly limited, for example, carbonate-based, ester-based, ether-based, ketone-based, organosulfur-based, organophosphorous ), Aprotic solvent, and combinations thereof.

The electrolytic salt refers to dissociation into a cation and an anion in a water or non-aqueous organic solvent, and is not particularly limited as long as it can deliver lithium ions in a lithium secondary battery, and can be selected generally used in the art.

The concentration of the electrolytic salt in the electrolytic solution may be 0.1 M or more and 3 M or less. In this case, charge and discharge characteristics of the lithium secondary battery can be effectively expressed.

The electrolyte may be a solid electrolyte membrane or a polymer electrolyte membrane.

Materials of the solid electrolyte membrane and the polymer electrolyte membrane are not particularly limited, and those generally used in the art may be employed. For example, the solid electrolyte membrane may include a composite metal oxide, and the polymer electrolyte membrane may be a membrane provided with a conductive polymer inside the porous substrate.

The positive electrode means an electrode that accepts electrons and reduces lithium-containing ions when the battery is discharged from a lithium secondary battery. Conversely, when the battery is charged, it acts as a negative electrode (oxidizing electrode), oxidizing the positive electrode active material to release electrons and lose lithium-containing ions.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

In this specification, the material of the positive electrode active material of the positive electrode active material layer is not particularly limited as long as it is applied to a lithium secondary battery together with the negative electrode to reduce lithium-containing ions during discharge and oxidize during charging. For example, it may be a transition metal oxide or a composite material based on sulfur (S), specifically LiCoO ₂ , LiNiO ₂ , LiFePO ₄ , LiMn ₂ O ₄ , LiNi _x Co _y MnzO ₂ (here, x + y + z = 1), Li ₂ FeSiO ₄ , Li ₂ FePO ₄ F, and Li ₂ MnO ₃ .

In addition, when the positive electrode is a composite material based on sulfur (S), the lithium secondary battery may be a lithium-sulfur battery, and the composite material based on sulfur (S) is not particularly limited, and in the art. It is possible to select and apply a commonly used anode material.

The present specification provides a battery module including the lithium secondary battery as a unit battery.

The battery module may be formed by stacking with a bipolar plate provided between two or more lithium secondary batteries according to one embodiment of the present specification.

When the lithium secondary battery is a lithium air battery, the bipolar plate may be porous to supply air supplied from the outside to the positive electrode included in each lithium air battery. For example, it may include porous stainless steel or porous ceramic.

The battery module may be specifically used as a power source for electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, or power storage devices.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and technical scope of the present invention. It is natural that changes and modifications fall within the scope of the appended claims.

Example 1: Lithium electrode comprising Cu matrix and PVDF

(1) Lithium electrode manufacturing

Polyvinylidene fluoride (PVDF) was coated on one side of a silicone-based release film (SKC Hass) to a thickness of 200 nm to form a PVDF coating layer.

Cu was deposited on one surface of the PVDF coating layer. As the Cu is vacuum-deposited on one surface of the PVDF coating layer, Cu particles penetrate the PVDF coating layer and enter into the inside, so that the Cu particles are electrically connected to each other inside the PVDF coating layer, and a Cu matrix in the form of a 3D structure having a space formed therein Formed. At this time, the weight ratio of Cu and PVDF was set to 50:50.

Thereafter, the PVDF coating layer on which the Cu matrix was formed was transferred to one surface of a 20 μm lithium metal to prepare a lithium electrode.

The lithium electrode was impregnated with the electrolyte, so that the electrolyte penetrated the PVDF coating layer, so that the PVDF coating layer formed a gel-like ion conductive electrolyte. The electrolyte was added with 5% by weight of fluoroethylene carbonate (FEC) as an additive to a solution in which lithium salt LiPF ₆ 1.3M was mixed with a solvent (EC: DEC = 1: 1 (v / v)) (EC: ethylene carbonate, DEC: Diethyl Carbonate). At this time, the uptake amount of the electrolyte solution was set to 35% by weight compared to 100% by weight of PVDF.

The finally manufactured lithium electrode has a structure in which a protective layer is formed on one surface of a lithium metal, and the protective layer is in a form in which PVDF is formed on the inner space and surface of the Cu matrix.

(2) Lithium secondary battery manufacturing

Using the prepared lithium electrode, a Li / separator / Li Symmetric Cell was prepared. At this time, the separator was used LC 2001 of SK innovation.

Example 2: Lithium electrode comprising Ge matrix and PVDF

A lithium electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that Ge was used instead of Cu.

Comparative Example 1: Lithium electrode with PVDF coating layer formed as a protective layer

A lithium electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that a 200 nm thick PVDF coating layer was formed as a protective layer.

Comparative Example 2: Lithium electrode without protective layer

A lithium electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a protective layer was not formed on the lithium metal.

Experimental Example 1

The lithium secondary batteries prepared in Examples and Comparative Examples were charged and discharged at a current of 0.5 mA / cm 2 and a capacity of 1 mAh / cm 2 to measure life characteristics, and the results are shown in Table 1 below.

	Protection layer	Protective layer			Electrical conductivity of electrically conductive materials (S / cm)	Short occurrence time (cycle)
		Electrically conductive matrix	Ion conductive electrolyte
		Electrically conductive material	Ion conductive polymer	Electrolyte
Example 1	○	Cu	PVDF	EC: DEC = 1: 1 (v / v) LiPF 6 1.3MFEC 5 wt%	5.8 x 10 7	220
Example 2	○	Ge	PVDF		1.0 x 10 2	140
Comparative Example 1	○	-	-		-	100
Comparative Example 2	X	-	-	-	-	92

As shown in Table 1, Examples 1 and 2, which are lithium secondary batteries including a lithium electrode having a protective layer including an electrically conductive matrix and an ion conductive electrolyte, have a shorter generation time than Comparative Examples 1 and 2 It can be seen that the life is improved.

Although the present invention has been described above by way of limited embodiments and drawings, the present invention is not limited by this, and is described below by the person skilled in the art to which the present invention pertains, and the technical idea of the present invention. Of course, various modifications and variations are possible within the scope of the equivalent claims.

[Description of codes]

10: lithium metal

20: protective layer

30: electrolyte

Claims (12)

1. Lithium metal: And in the lithium electrode comprising a; protective layer formed on at least one surface of the lithium metal,

   The protective layer includes an electrically conductive matrix and an ion conductive electrolyte, a lithium electrode.
2. According to claim 1,

   The electrically conductive matrix includes one or more electrically conductive materials selected from the group consisting of electrically conductive metals, semiconductors, and electrically conductive polymers, lithium electrodes.
3. According to claim 2,

   The electrically conductive metal is at least one selected from the group consisting of copper, gold, silver, aluminum, nickel, zinc, carbon, tin and indium,

   The semiconductor is at least one selected from the group consisting of silicon and germanium,

   The electrically conductive polymer is PEDOT (poly (3,4-ethylenedioxythiophene)), polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene and polyphenylene At least one lithium electrode selected from the group consisting of poly (thienylene vinylene).
4. According to claim 1,

   The ion conductive electrolyte is to include an ion conductive polymer, lithium electrode.
5. The method of claim 4,

   The ion-conducting polymer includes polyethylene oxide (Poly (ethylene oxide): PEO), polypropylene oxide (Poly (polypropylene oxide: PPO), polyacrylonitrile (PAN)) and polyvinylidene fluoride (Poly ( vinylidene fluoride): one or more lithium electrodes selected from the group consisting of PVDF).
6. The method of claim 4,

   The ion conductive electrolyte may be a liquid or gel ion conductive electrolyte; Or a solid phase ion conductive electrolyte; phosphorus, lithium electrode.
7. The method of claim 6,

   The liquid or gel-like ion-conducting electrolyte comprises a lithium salt, a non-aqueous solvent and an electrolyte containing an additive, a lithium electrode.
8. The method of claim 7,

   The lithium salt is LiCl, LiBr, LiI, LiNO ₃ , LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, 4-phenyl lithium borate And at least one lithium electrode selected from the group consisting of lithium imide.
9. The method of claim 7,

   The additive is at least one selected from the group consisting of fluoroethylene carbonate (FEC), 1,3-propanesultone (1,3-PS) and vinyl ethylene carbonate (VEC), lithium electrode.
10. According to claim 1,

    The protective layer is an ion conductive electrolyte is formed on the inside and the surface of the electrically conductive matrix, lithium electrode.
11. According to claim 1,

    The electrically conductive matrix; And an ion-conducting polymer contained in the ion-conducting electrolyte; a weight ratio of 3: 7 to 7: 3, a lithium electrode.
12. A lithium secondary battery comprising the lithium electrode of any one of claims 1 to 11.

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